Mysterious piles of silvery grains in the desert

I like my social media connections very much, even if I do spend much too much time with them. On Facebook, BugGuide and Flickr I am connected to many knowledgeable experts in their fields and creative artists whose work I would otherwise never get to see.
I bring in my own contributions by helping local friends to solve their bug mysteries and identify the occasional lizard or bird.
A couple of weeks ago, I ran into a mysterious 'thing' myself. Actually, I found 'it' by kicking over a long dried cow pie, left in the state land behind our property by cattle that was moved out years ago. But I still find the occasional bug or banded gecko hiding in those places ...

This time the ground under several pies was covered with a grainy silver gray substance. The grains were very regular in size. In my macro photos they also appeared sculpted or textured. There were tiny silver fish running between them.

Silver fish eggs? No, every female lays up to 100 in her live time. It would have taken a village or a small town of silver fish to produce this many.

I put the image on Facebook rather than BugGuide because I wasn't sure that this had anything to do with insects.
Rich Hoyer immediately suggested seeds.

After the monsoon the desert was covered in a golden blanket of chinch weed. It's still blooming.   Many plants are already setting their papus-equipped fruit.

There would have been enough chinch weed seeds to collect, but those seeds are long and dark. After knowing what to look for I actually found about three of them among thousands of the shorter ones. There is one in the bottom right corner.

So what are the little grey seeds? James Trager suggested mint or euphorbia. After searching for a long time I came up with one plant that is probably in the mint family, but it is by far too uncommon.
Euphorbia then?

 I sent the photo to Tom VanDevender who has a seed collection for the Sky Island Alliance. I had even discovered a seed pod in one of my photos by now. Yes, they are euphorbia seeds and can the alliance please keep the nice photo for their files? Sure.

 But now I wanted to know the exact species. There are patches of a small brownish green, prostrate weed all over, but I had completely ignored it because it is so unremarkable and common. Does it even flower? Of course. I just needed a magnifying glass to see flowers and even little seedpods.

Probably Chamaesyce/Euphorbia micromera

 Actually, I soon recognized that there were two species around and posted photos of both on FB.  FB friend Burr Williams from Texas then linked my query to the young botanist Nathan Taylor who actually specializes in 'prostrate euphorbia species' and who was glad and excited to help!

Chamaesyce/Euphorbia abramsiana

 He not only identified the two spp from our state land but also a third that had been in my files because of a bee fly that uses its tiny flowers.

Euphorbia/Chamaesyce albomarginata with Hemipenthes lepidota Cochise Co. AZ

So now think we know that the grainy stuff is indeed Euphorbia seeds, but how did it get under the old cow pie? Many FB friends speculated. The idea that the cow fed on the plant and then somehow segregated the seeds to expel them in a dense layer seemed unlikely. Also the seeds were fresh and the cow gone for years. It also wasn't wind drift that had piled up, because the cow pie was still sticking to the ground before I kicked it.

Of course, any collection of small seeds suggests ants. Many plants actually equip each seed with a little treat called elaiosome,, so ants will carry the seeds to their nests, eat the treat and throw out the seed, still intact (Seed dispersal by ants (myrmecochory).
Our two great collectors in the area are Veromessor pergandei and  Pogonomyrmex rugosus. But none of them seemed to be around in the vicinity of the cow dung. Also, both species tend to bring their harvest to their nests rather the storing it somewhere else.  

Under many dry cow pies, there are colonies of Solenopsis xyloni (Southern Fire Ant) a little ant that I only knew as a fierce predator. But James Trager told me that they also collect seeds. So I went through my pictures again. Yes! There are the little guys working among the seeds, and there even seems to be an entrance to a deeper more subterranean part of their nest on the left side. Remember that the entire seed pile was originally under ground, or at least under a very old piece of cow dung.

There, mystery solved! Net working and discussing worked. Except: what are those amber colored seeds? we thought that they were gray ones that had lost a waxy outer coating. looking more closely, I do not think so anymore. So? Suggestions?

Saguaro Fruit: Mid Summer Sustenance

In my early June blog, I still had to use Doris Evan's saguaro fruit image from the east side of the Tucson Mountains because here in Picture Rocks the saguaro fruits were still green and closed.

Since then the fruits on our 'House Saguaro' first blushed on the outside, then split open and revealed their signal red inside: ripe! Birds, come and get sweet pulp and seeds! For weeks this bounty (and 2014 seems to be a particularly good year)  has been a steady source of nutrition for the resident animals and entertainment for us.

Tiny Verdins and families of House Finches regularly gorged themselves,  Cactus Wren and Curved Bill Thrasher parents were feeding their fledgeling young. Gila Woodpeckers and Gilded Flickers were too shy for good photographs this year, but noisily announced their presence while peaking around from the back. 

A Mourning Dove and a White Winged dove actually moved into the big cactus, their nests not even two feet apart but separated by one of the massive arms. By now the first set of chicks has flown out and the White Wings have started another batch of eggs. 

Even a pair of ravens brought 4 youngsters around, causing the other birds to break into loud, angry mobbing. The fruits are surprisingly sturdy, safely supporting those huge birds. The tall columnar cacti firmly hold onto their fruit, even after they are ripe and split open. Why?
The saguaro relies on zoochory (seed dispersal by animals) and especially on the dispersal by birds.
Birds have great color vision and can easily reach the top of the saguaro. The spontaneous splitting of the tough skin allows them access. They devoure the sweet pulp with the seeds, fly good distances, and then excrete the unharmed seeds.

Photo by Rich Hoyer

Rodents and ants would also carry some seeds around, sometimes bury them and forget their cache, so that later clusters of seedlings might emerge. But their action radius is limited compared to that of birds and they also tend to chew the seeds and destroy them. So for the columnar cactus it 'makes sense' to keep the fruits out of reach of the ground dwellers and instead allow easy access to gently digesting long distance travelers who lack gnawing tools by presenting the open fruits on top of the inaccessible column (compare to the different 'strategy' of the barrel cactus)   (Quotation marks indicate my flippant teleological descriptions of intricate evolutionary adaptations.)
After the birds had their turn, the fruits are finally falling and landing on  the ground with an audible plop. The star-shaped hulls usually still contain enough seeds and pulp to attract some  hungry quail that don't like the height of the saguaro top and many ants, flies, flightless beetles and rodents.

So the food chain of the desert floor is set into motion. Soon photo-shy Tiger Whiptails arrive to hunt for insects.

Our resident rattler seems to patrol at least once a day. Who knows what goes on at night when the packrat collects the hard dry hulls to decorate her nest? Coyotes and bobcats are hanging around more than usually. The opportunistic coyotes will of course take the dinner as well as the diners. Jan Emming showed in a facebook post that canines can be pretty efficient seed dispersers.

The packrat takes empty hulls and dry flower stalk to its midden

At dusk I surprised a Cottontail and a Mourning Dove snacking on the sweet stuff

One can hardly overestimate the importance of the saguaro fruit harvest for the desert dwellers who have by now endured over 3 months without measurable rainfall. In addition, many young animals were born in spring and became independent of their parents at this time, just when the heat becomes merciless and the monsoon rain is still only a cloudy promise at the horizon. Saguaros have horded the winter rains in their immense succulent bodies and thus have the ability to offer (for dispersal services) nutrition and some fluid during the season when it is needed most.

Stella Tucker harvesting Saguaro fruit.  Watercolor

The Tohono O'odam are the desert people most intimately acquainted with the saguaro. To them the ripening fruits on the saguaros signaled the beginning of celebrations and prayers for a good rainy season. They use the long ribs of dead saguaros, with a small cross piece attached to one end, to push the fruit down when they are ripe, but not yet open. Then they split them with the built-in knife which is the hard, dried flower that is still attached to the fruit. Saguaro pulp was one of the few sweet treats available to the desert people. Some of it was made into preserves, but most of it was collected in ollas with water and allowed to ferment to make the ritual saguaro wine, an integral part of rain dance ceremonies that are held to ensure another life-bringing monsoon.
Years ago Stella Tucker, a Tohono O'odam story teller and historian, showed me how the long collecting pole is used and I found out how hard it is to dislodge the fruits before their time.  In my painting Stella is holding the saguaro rib, and the back of her shirt is patterned with petroglyphs depicting the harvest.